Ventricular fibrillation is a potentially life-threatening cardiac condition. Most conventional defibrillation devices, whether external or implantable, treat ventricular fibrillation with a cardiac stimulus of quite high energy. For example, external devices typically use an energy level in excess of approximately 200 joules and implantable devices typically use an energy level in excess of 10 joules. Such stimuli can be quite painful when delivered to a conscious patient. For an implantable device, such stimuli can also greatly impact the device's limited power supply. Further, while an implantable device requires lesser energy level stimulus for defibrillation compared to an external device, the consequences on size, weight and/or shape of an implantable device capable of producing a 10 joules stimulus is significant.
Recent studies using mathematical models, non-human animals and/or external devices have shown that at the onset of ventricular fibrillation, the number of reentry wavefronts may be low, for example, on the order of 1 or 2, similar to a monomorphic tachycardia. During subsequent activations, the fast activation rate of reentry wavefronts compared to sinus rhythm wavefronts causes an increase in electrical heterogeneity of the cardiac tissue, which, in turn, can cause an increasing number of wavefronts through wavefront breakup. Indeed, wavefront breakup may play an important role in the acceleration of an arrhythmia into a stable ventricular fibrillation. The time that is takes for such a transition to occur may be expected to vary, for example, from patient to patient, and experimentally from model to model.
As described herein, various exemplary methods, systems and/or devices aim to detect ventricular fibrillation or precursors thereof at an early stage, for example, prior to stabilization. Based on such detection, such exemplary methods, systems and/or devices may deliver one or more stimuli to terminate, disrupt or otherwise convert physiological processes related to wavefront breakup.